5.0 Mustang & Super Fords
2013 Shelby GT500 Chassis Development - Total Package
The 2013 Shelby GT500 is much more than a 662hp 5.8
The 662hp GT500 has hellish heat rejection to battle. This is especially true at high speeds, when the engine is working hard, and why SVT took a two-tier approach to cooling the new Shelby. That is, GT500s in standard duty cool just fine in base form, while the cars that are run at "... high speeds for a long time" are the reason for Track Cooling.
Erin Gibb, the SVT engineer tasked with working out the cooling details, started with the supercharger's charge air cooler (intercooler). This took some doing. Apparently three systems were tried before everyone was happy, but the result is a massively larger heat exchanger and a coolant pump with twice the flow capacity.
The larger exchanger and pump yield a huge 45-percent increase in heat rejection, which fully manifests itself at the road course. Whereas early GT500s would heat-soak after a few laps, then pull ignition timing for detonation protection--positively murdering horsepower in the process--the '13 GT500 laps continuously with only a minor reduction in power. We don't think you'll notice it. The car is consistent at the dragstrip, too.
By comparison, relatively little was done to the engine-cooling hardware. The radiator is a carryover (save for removing the trans cooler lines), as is the water pump, but after computer analysis and wind tunnel work, the electric radiator fan has gone from six to seven blades and the fan motor from 400 to 450 watts of power. Also, the gaps around the radiator were closed to conduct air through the radiator instead of the many pathways around it.
Where the big cooling push came was getting air to and through the GT500's up to six heat exchangers. What SVT saw in its computational flow dynamics and wind tunnel testing was they needed more air--and high-quality air--flowing through the heat exchangers. By high-quality air, they cite "first air," the direct ram air not pre-heated by some other radiator.
Thus, as much as possible, the various heat exchangers were given their own air paths, and considerable work was done to the front fascia and grille. In the end, the grille was mainly eliminated--all those little eggcrate shapes kill airflow--and various ducts were added to direct ram air to the engine oil and differential Track Cooler radiators.
Cooling at high road speeds was augmented by four air flaps in the lower corners of the fan shroud. They are not spring-loaded--gravity holds these simple flaps shut because they pivot fairly close to their upper edge, but at around 70-mph ram air is sufficient to open them, increasing ram air flow to the radiator. This bypasses the radiator fan, but at high road speeds the fan is more of an obstruction to airflow than a help, so the flaps are a definite gain.
These cooling changes seem straightforward now, but developing them took considerable CFD and tunnel time. The engineers report the computer analysis can only get a design so close before real-world development or wind-tunnel work is required to vet the final three or so designs. Also, effort was put into looking for useful air paths for exiting all this ram air out of the engine compartment, but in the end, the traditional waypath out the bottom rear of the compartment proved the best.
Several years of Mustang and GT500 development meant the basic unibody needed nothing as the foundation for a 200-mph car, the suspension was well understood and wanted only a greater performance personality. But at the same time, SVT knew they needed a wider performance span, something they could get with cockpit-adjustable shocks.
Fortuitously, Bilstein was introducing a new, affordable DampTronic dual-mode shock, and it was soon incorporated into the '13 GT500's optional suspension tune, the Performance Package. Between the standard and Performance Pack suspensions, the GT500 services the broad mandates of SVT customer goals of street cruising, track lapping, and dragstrip action. The base suspension uses Tokico twin-tube shocks, while the Performance Pack utlizes the higher-rate springs, sway bars, and adjustable Bilstein DampTronic shocks (re-styled wheels and the excellent Torsen torque biasing differential are also included).
To get started building grip, SVT's chassis dynamics team, headed by Eric Zinkosky, canvassed industry partners, including Ford Racing and NASCAR teams, plus they looked far outside the box when it came to test and development tools. With a car of the GT500's capability, most development drives are done on race tracks. Eventually the GT500 test mules ran on seven road courses and four dragstrips, including the famed Nurburgring in Germany, and the Nardo road course and high-speed tracks in Italy.
Some of the test-track data was recovered, and in conjunction with Ford Racing, was re-run for four days on the multi-million-dollar, seven-post chassis rig at Roush Fenway Racing in Concord, North Carolina. The ability to instrument and quantify pitch and roll information on the shake rig is its primary contribution.
From a ride and handling standpoint, the GT500 coupe and convertible are somewhat different cars. In general, the more rigid coupe was tuned by Gene Martindale for maximum performance tempered by reasonable comfort, while David Harmison ensured the convertible was comfortable but with SVT-appropriate handling.
For an enthusiast, daydreams of running the Nurburgring and Nardo tracks are compelling, and as Gene, who did much of that driving, happily admits, much of it is a blast. But it's also serious work, as he points out when he says initially he thought the 'Ring was going to be little more than a marketing ploy, but once there he found the famed German track offered pretty much all the corners, hills, and straights found across North American tracks but in one lap. Plus it has heaves and jumps not available here. The 'Ring turned out to be a challenging, effective development tool, and it was visited twice by the GT500 team.
Other times development driving isn't the romance we envision. SVT guidelines call for "significant" steering inputs at all speeds the vehicle is capable of to validate chassis behavior. Well, do you want to be the guy tasked with making "significant" steering inputs at 200 mph? Gene had to do just that at Nardo.
There is far more to the GT500 technical development than we're able to present here, but we hope to at least hint at the effort SVT has made to make the GT500 a machine designed to please discriminating drivers no matter how adventurous they get. For a car aimed at both the street and track, that's a lofty order, but the '13 Shelby GT500 is up to the task. 5.0
Horse Sense: Ford truly bends over backward to help us get our stories. Our only complaint is there is never enough space in the magazine to present all the fascinating tidbits that come from a visit to Ford. This is especially true of the Special Vehicle Team--a motivated, skilled and enthusiastic group any 5.0 Mustangs & Super Fords reader would love to spend the day with, especially at the track.